Ammonium nitrate explosive



United States Patent ()filice 3,091,559 Patented May 28, 1963 3,091,559 ONIUM NITRATE EXPLGSIVE COMPOSITION Harold E. Staadt, Tulsa, Okla, assignor to The Dow Chemical Company, Midland, Mich, a corporation of Delaware No Drawing. Filed Jan. 5, 1959, Ser. No. 784,900 3 Claims. (Cl. 149-60) This invention relates to an improved ammonium nitrate explosive composition and more particularly concerns a cap-insensitive ammonium nitrate explosive composition.

It has been a desideratum in the explosives ant to formulate and compound explosive compositions which may be safely handled and transported, yet are reliably and eflectively detonated. To fill this need various ammonium nitrate explosive compositions have been proposed but these have been generally cap-sensitive and have required boosters, such as *gelatine dynamite, spaced throughout a large load to insure good propagation.

It is an object of the present invention to provide a cap-insensitive ammonium nitrate explosive composition which may be safely handled and transported with little danger of shock initiation yet may be detonated eifectively by a shaped charge using the Munroe jet principle.

It is another object of the invention to provide a capinsensitive ammonium nitrate explosive composition which upon proper initiation produces a detonation of useful magnitude and force.

A still further object of the invention is to provide a low-cost cap-insensitive ammonium nitrate explosive composition which is adapted to be readily compounded near the point of use.

Other objects and advantages of the invention will become apparent to one skilled in the art upon becoming familiar with the following description and claims.

These and other objects are attained upon admixing ammonium nitrate, itself cap-insensitive, with ammonia and water in proportions hereinafter more fully described and further illustrated by examples of the invention. All proportions herein given in percent are to be understood as percent by weight unless otherwise indicated.

The explosive composition of the invention may be compounded from particulate ammonium nitrate, ammonia and water. However, in the preferred manner of preparing the composition, particulated ammonium nitrate is admixed with anhydrous Divers liquid and water or with an aqueous ammoniacal solution of ammonium nitrate. Divers liquid is a saturated or nearly saturated solution of ammonium nitrate in anhydrous liquid ammonia containing generally about 70 to 80 percent of ammonium nitrate depending on the temperature of the solution and the manner of preparing it. An ammoni'acal solution of ammonia nitrate containing from 0.6 to 30 percent of Water is referred to herein as an aqueous 'ammoniacal solution of ammonium nitrate. Such aqueous solutions containing ammonium nitrate and ammonia in the proportions of about 1.8 to 1 are commercially available at lower cost and are easier to handle than the anhydrous solution because of the reduced vapor pressure of the ammonia therein in the presence of water. As an example a solution consisting of 60 percent of ammonium nitrate, 34 percent of liquid ammonia and 6 percent of Water is commercially available as the trademarked product Spensol D.

Solid particulated ammonium nitrate used in preparing the composition of the invention may be of fertlhzer 2 grade as well as of explosive grade ammonium nitrate. While the explosive grade material tends to detonate with slightly greater force on an equal weight basis, it is gen erally more economical to make up for this by using a slightly greater amount of fertilizer grade ammonium nitrate.

Fertilizer grade ammonium nitrate generally contains various additives or fine particulate coatings inhibiting calcing and promoting free-flowing characteristics of the material. Ammonium nitrate as referred to herein is defined as ammonium nitrate containing up to 3 percent of various additives such as wax, diatomaceous earth and chalk in addition to a moisture content ranging up to about 1 /2 percent. Either the granular or prilled form of the nitrate salt are satisfactory.

To avoid making cap-sensitive mixtures the composi tion is best prepared from ammonium nitrate having particle sizes mainly in the range of 8 to 100 mesh, fines passing 100 to 200 mesh tending to increase the sensitivity of the mixture. An example of a satisfactory granular ammonium nitrate readily obtained commercially has the following sieve analysis.

Table I No. of No. of Percent Sieve 1 Sieve Re- Retained Passed tained On 12 3 12 20 34. 4 20 3O 16. 4 30 40 13. 4 40 60 14. 4 60 8. 4 80 1. 9 100 200 6. 4 200 pan 4.4

1 Sieves of the 3.8. Sieve Series, U.S. Bureau of Standards.

An example of a satisfactory prilled ammonium nitrate which is commercially available has the following sieve analysis:

Table II No. of No. of

Sieve Sieve Percent Passed Retained Retained 35 Pan Trace The above examples are not intended to be limitative but indicative of the nature of commercially available ammonium nitrate.

The hereinabove described components of the explosive mixture of the invention may be combined in various proportions, the proportions ranging from 55 to 97 percent of particulated ammonium nitrate, from about 3 to 54 percent of Divers liquid and from 0.3 to 6 percent of Water. The corresponding range of values for total ammonium nitrate in the composition may vary from 80 to 99 percent of ammonium nitrate and for ammonia from 1 to 19 percent. The range of water content here described does not include the normal moisture content of particulated ammonium nitrate.

Mixtures containing from about 83 to 96 percent of ammonium nitrate, from 3 to 14 percent of Divers liquid and 0.3 to 6 percent of water are generally readily loaded into accessible boreholes or fissures in earth formations.

An explosive mixture of the invention containing from about 58 to 83 percent of ammonium nitrate, from 14 to 42 percent of Divers liquid and 0.5 to percent of water is to be preferred from pumping into a borehole as a slurry and is especially advantageously used in loading an elongated or upwardly sloping borehole or when it is desired to inject an explosive mixture into an earth or rock formation or ore body under high pressure conditions, such as up to 10,000 p.s.i. or greater.

If desired the explosive composition of the invention may be thickened upon admixing therewith from about 0.12 to 5 percent, based on the weight of the liquid phase, of a thickening agent such as methyl cellulose or gum karaya. Other suitable thickening agents are carboxymethyl cellulose, kava kava gum, guar gum, accroides gum, locust beam gum, balsam tolu natural, Irish moss, Iceland moss and Separan NF (a high molecular weight polyacrylamide). The foregoing thickening agents are generally recognized as water soluble high molecular weight natural or synthetic gums which are capable of forming sols when admixed with water. The effects of various thickening agents on the viscosity of an aqueous ammoniacal solution containing 60 percent of ammonium nitrate, 34 percent of ammonia and 6 percent of water were determined and the results are listed in Table III.

Table III Viscosity Weight of solution Thiokener percent of containing Thickener added thickener p None... 7. 5 Carboxymethyl cellulose extra high 5 100, 000 Guar gum 5 100, 000 Kava Kava guru 5 450 Accroides gum--. 5 120 Locust bean gum 1 18 Do 5 100, 000 Balsam Tolu natural g-u 1 Irish 5 60 Iceland moss 5 42 Separan NP 10.-.. 5 140 Methocel 70 HG 0. 125 10 D 25 19 5 77 1 315 5 95, 000 Karaya gum- 0.125 18 D 28 142 1 395 5 4, 000

Compositions containing these thickening agents in admixture 'are found to hold particles of ammonium nitrate in suspension for a longer period than do unthickened compositions thus retaining greater homogeneity. As a result the mixtures detonate at somewhat more reproducible velocities than unthickened mixtures or slurries. Thickened slurries are somewhat safer to handle in that uniform dispersions are less sensitive to initiation by shock than are the solids settling out of a slurry or mixture. Thickened slurries possess the additional advantage that they lose less ammonia vapor when exposed to atmospheric conditions as in open containers and thus are less noxious to handle.

In detonating the explosive mixture of the invention the load or charge of the said mixture is placed in the desired location usually in the confinement of a bore hole. A shaped charge such as a Jet Perforator used in perforating oil well casings, loaded with about one ounce of RDX explosive is armed with a suitable initiator therefor, such as a No. 8 electric blasting cap and placed next to the load. The wire lead from the blasting cap is run to a remote control point and, if desired, a sand or gravel tamp is placed over the load and initiators. The load is then fired electrically from the remote control point. In detonating a large load, such as one loaded into an elongated bore hole, only one shaped charge is needed to detonate the entire load though more than one may be used. In initiating an explosive mixture by means of a shaped charge, a self-contained time-controlled firing mechanism may be used if desired in place of the manual controls referred to above.

The compositions of the invention possess the advantage that they may be slurries in an additional proportion of Divers liquid and water, for example in proportions such that the ratio of solid to liquid phases is about 1:1, and pumped into a bore hole in an earth formation and there allowed to settle out to a detonable mixture. Or a solid phase may be filtered or screened out to form a detonable mixture when the composition is placed under pressure against an earth formation permeable to the liquid phase under pressure.

To demonstrate the insensitivity but inherent detonability of the ammonium nitrate explosive mixture of the invention various embodiments of the invention were prepared and tested. In each test a 10 pound quantity of explosive mixture was formulated of a particulated fertilizer grade ammonium nitrate and a solution of Divers liquid plus water in the proportions shown in Table II. The individual ten pound portions were in each case mixed in a separate polyethylene plastic bag of sufiicient size to readily hold the ten pound quantity. The various components of the mixture were Weighed into the bag, the bag closed, and the contents mixed by kneading the bag with the hands. The fertilizer grade ammonium nitrate contained about 0.7 percent of wax, 1 percent of diatomaceous earth, and 0.3 percent of chalk. The particle size of the ammonium nitrate was such that 94 percent by weight of the particles passed a 20 mesh sieve and percent by weight were retained on a mesh sieve. The aqueous ammoniacal solutions of ammonium nitrate contained about 1.8 parts by weight of dissolved ammonium nitrate to 1 part by weight of liquid ammonia in addition to the water present. The proportions of water varied from about 6 to 30 percent of the total weight of the solution.

The prepared mixtures were loaded into individual shallow bore holes drilled four feet deep and four inches in diameter in clay soil. Successive bore holes were spaced about twenty feet apart. The loading of each hole was accomplished by first placing an initiator, such as a blasting cap, or a shaped charge armed with a blasting cap, in the bottom of the hole and running lead wires to the firing control switch. Each shaped charge used was positioned with the jet end facing upwardly. The explosive mixtures in the plastic bags were lowered into respective test holes, the bag thus being immediately over the initiator. Sand was used as a tamp, the hole being filled from the bag to ground level with sand. Detonation of the mixture was attempted by closing the firing switch thus setting off the initiator at the bottom of the hole. In a comparison test in the form of a blank one hole was loaded solely with a 10 pound quantity of fertilizer grade ammonium nitrate and an initiator.

The magnitude of the detonations obtained were determined by measuring the size of crater produced. While the crater size along is not indicative of the amount of earth formation that is broken up, it does give an indication of the Work potential of the mixture detonated. The crater size herein reported shows how much material was thrown sufficiently so as not to fall back over the test hole. Test conditions and results are summarized in Table IV.

Table IV with conventional explosives varied amounts of 60% I dynamite each with a No. 8 electric blasting cap therefor Initiamr g g it were placed in shallow test holes 4 feet deep, tamped L with sand and detonated. 5 lbs. of dynamite so loaded Test 5 and detonated produced a crater 5 feet in diameter and No. RDX Ex- FGAN, S.D., Blasting plosivein 1.5 feet deep; 10 lbs. of dynamite produced a crater 8 percent 1%; Cap gfig ggg Depth 53 feet in diameter and 1 foot deep; while 25 lbs. of dyna- Charge mite produced a crater 11 feet in diameter and 5 feet deep. 38 :82: 33: 10 Additional tests were carried out in the same manner 1 1 9 described above to demonstrate the detonability and l 1 7 I none none none worl potential of other embodiments of the mventron. 0 0 11011; Various solutions of Diver s liquid plus water were em- 1 3 ployed and in some cases additional water was added g 15 to the mixtures. The compositions of the mixtures and 33 '3 8 the type of initiators used and the test results are listed 1,4 none none in Table V. FGAN=ferti1i er grade ammonium 13mm 'hiese results show the detonability of a range of com- S.D.=Spensol D. i i

Table V Explosive Composition Initiator Crater Dimensions, it.

Test FGAN, No. percent RDX E);- Solution of Divers Added Blasting plosive 1n liquid+water H2O, cap ounces, Depth Diameter percent shaped charge 1s 94 5 %H,0) 1 #8 EBO 1 1 8 14."- 89 10 (6% H10) 1 #8 EBO 1 1 5 80 (6% H20 #8 EBG 3% 1 5 16 80 20 (6% H20)..-" #8 E130". 3% 1 5 17 75 (6% H10). #8 EBO 3% 1 5 18 70 (6% H10). #8 EBG 3% 3 10 19---- 30 (6% H20). #8 EBO 3% 3 15 20 60 40 (6% H9O) #8 EBO 3% 3 11 21- 95 5 (9.6% H20). 8# EBC. 1 1 5 22 15 (9.6% H20)" #8 EBC 1 1 1. 5 23.-.- 10 (14.5% H20). #8 EBO 1 1 8 24 85 15 (14.5% H20)- #8 EBC--. 1 1 5 25 5 (19.7% H20)" #8 EBC 1 1 7 26..-. 95 5 (30.3% H9O) #8 EBG 1 1 5 FGAN-fertilizer grade ammonium nitrate.

The results tabulated in Table IV show that the explosive mixture of the invention is not sensitive to a No. 8 electric blasting cap but that the mixture is more sensitive to detonation than ammonium nitrate alone.

In order to compare the composition of the invention 50 phase with solid ammonium nitrate.

The compositions tested and the test results are summarized in Table VI.

Table VI Crater Explosive Composition Initiator Dimensions, it.

Test No. Gum RDX Karaya, Explosive FGAN, S.D., Percent Blasting in ounces Depth Diameter Percent Percent (based cap Shaped on wt. charge 95 5 #8 EB O 3% 2 10 95 5 #8 EB C i 3% 3 11 90 10 #8 EBC--. 3% 4 10 90 10 #8 EEC- 3% 1 10 85 15 #8 EB O- 3% 2 8 85 15 #8 EBO 3% 3 9 80 20 #8 EBO 8% 1 5 80 20 #8 EBO. 3% 2 8 75 25 #8 EB O 3% 1 7 7O 30 #8 EB O 3% 2 10 70 3O #8 EB 3% 1.5 9

70 30 #8 EB C- -i 3% 4 9 FGAN =fertilizer grade ammonium nitrate. S.D.= Spensol D The results show the detonability of a range of compositions.

The compositions of the invention possess the additional advantage that they are but little affected by moist environment and can even tolerate a small amount of connate water.

What is claimed is:

1. An explosive composition consisting essentially of an admixture of from 55 to 97 percent by weight of particulate ammonium nitrate having a particle size of from about 8 to 100 mesh, from about 3 to 54 percent by weight of Divers liquid, and from 0.3 to 6 percent by weight of water and containing in admixture from about 0.12 to 5 percent, based on the weight of the Divers liquid plus the weight of water present, of a thickening agent consisting of a water soluble gum which is capable of forming a sol when admixed with water.

2. An explosive composition consisting essentially of an admixture of from 55 to 97 percent by weight of particulate ammonium nitrate having a particle size of from about 8 to 100 mesh, from about 3 to 54 percent by weight of Divers liquid, and from 0.3 to 6 percent by weight of water and containing in admixture about 0.25 percent of gum karaya, based on the combined weight of Divers fluid plus the weight of water present.

References Cited in the file of this patent UNITED STATES PATENTS 2,168,562 Davis Aug. 8, 1939 2,393,594 Davis Jan. 29, 1946 2,657,977 Stengel et al Nov. 3, 1953 2,703,528 Lee et al Mar. 8, 1955 2,860,041 Grifiith et a1 Nov. 11, 1958 2,903,969 Kolbe Sept. 15, 1959 OTHER REFERENCES Bebie: Manual of Explosives Military Pyrotechnics and Chemical Warfare Agents, The Macmillan Co., New York (1943), P. 25.

Dougherty: Chem. Eng. Progress, vol. 53, No. 10,

25 October 1957, pp. 589-92; note page 490. 

1. AN EXPLOSIVE COMPOSITION CONSISTING ESSENTIALLY OF AN ADMIXTURE OF FROM 55 TO 97 PERCENT BY WEIGHT OF PARTICULATE AMMONIUM NITRATE HAVING A PARTICLE SIZE OF FROM ABOUT 8 TO 100 MESH, FROM ABOUT 3 TO 54 PERCENT BY WEIGHT OF DIVER''S LIQUID, AND FROM 0.3 TO 6 PERCENT BY WEIGHT OF WATER AND CONTAINING IN ADMIXTURE FROM ABOUT 0.12 TO 5 PERCENT, BASED ON THE WEIGHT OF THE DIVER''S LIQUID PLUS THE WEIGHT OF WATER PRESENT, OF A THICKENING AGENT CONSISTING OF A WATER SOLUBLE GUM WHICH IS CAPABLE OF FORMING A SOL WHEN ADMIXED WITH WATER. 